The attack took place in Gandi Umer Khan area of Dera Ismail Khan district in Khyber-Pakhtunkhwa province.
The policemen were riding a bike on their way back from duty with a polio team when they were ambushed by the unidentified militants, killing them on the spot, police said.
The incident was the latest attack on efforts to root out the crippling disease in Pakistan, which is one of only three countries where polio remains endemic.
The Taliban have banned polio vaccinations in parts of the tribal belt till the US stops drone strikes. Tens of thousands of children have been left vulnerable by the ban.
Dozens of health workers and security personnel have died in attacks on polio vaccination teams in the northwest and the port city of Karachi.